Synthesis, characterization, and biological evaluation of novel xanthate ligands and their divalent metal complexes: DFT calculations and molecular docking studies

This study presents the synthesis of two novel xanthate ligands—potassium phenylethyl xanthate (L1) and potassium propyl xanthate (L2)—and their coordination complexes with Co(II), Ni(II), Cu(II), and Zn(II) ions. Comprehensive characterization—including elemental analysis, FT-IR, AAS, UV–Vis, and ¹H NMR spectroscopy—confirmed the bidentate coordination mode of the ligands. Conductivity measurements indicated that the complexes are non-electrolytic, while XRD data revealed crystalline formation (particle size 16–26 nm; crystallinity index 29–68 %), and magnetic susceptibility and electronic spectra adopting tetrahedral geometries. Antibacterial screening against E. coli, K. pneumoniae, S. aureus, and Streptococcus sp. revealed negligible activity for the free ligands (zones 1.5–4 mm; MIC >100 μg/mL). Metal coordination enhanced potency, with Cu(II) complexes showing the strongest effects (zones 10.5–27 mm; MIC 6.25 μg/mL), followed by Ni(II) and Co(II), while Zn(II) derivatives were least active. Compared with ciprofloxacin (zones 20–26 mm; MIC 0.781–3.125 μg/mL), Cu(II) complexes displayed competitive antibacterial performance, indicating their promise as alternative antimicrobial agents. Antioxidant potential, assessed via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, revealed that the Cu(II) and Ni(II) complexes achieved IC₅₀ (half-maximal inhibitory concentration) values between 55.0 and 77.4 μM, compared to 20.7 μM for ascorbic acid, indicating marked radical-scavenging ability. Molecular docking studies with human serum albumin (PDB 1H9Z) yielded binding affinities ranging from −4.0 to −9.2 kcal/mol, suggesting stable protein–ligand interactions. Density Functional Theory (DFT) investigations—addressing optimized structures, HOMO–LUMO energy gaps (3.044–4.756 eV), global reactivity parameters, and dipole moments—further substantiated the electronic stabilization conferred by metal coordination. Overall, this integrative experimental and computational study underscores the potential of these xanthate-based metal complexes as chemically stable and biologically active agents.